Engine cylinder and method of protecting the same against corrosion



1944. R. VAN DEVENTER 2, ,7

9 ENGINE CYLINDER AND METHOD OF PROTEC TING THE SAME AGAINST CORRO SION Filed Nov. 12, 1941 will tive layer despite all that is known Patented Oct. 3, 1944 AND METHOD OF PRO- TECTING THE SAME AGAINST CORRO- ENGINE CYLINDER SION Ralph E. Van Deventer, Detroit, Mich., assignor to Packard Motor Car Company, Detroit, Mich.. a corporation of Michigan Application November 12, 1941, Serial No. 418,835

7 Claims.

In the Production of internal combustion engines of ordinary type, particularly those in which the cylinders are formed in a cast metal block, it is seldom found feasible to protect the walls of the water passages against the corrosive action of the cooling water. Corrosion proceeds, but at a relatively low rate, and in the usual case the useful life of the engine is terminated because of ordinary mechanical wear. With internal combustion engines of other types, however, it' may be and frequently is highly desirable to provide the surfaces of the water passages with coatings of corrosion resistant materials in order that the useful life of the engine as a whole may not be limited by corrosion. This is particularly true in engines of the light-weight and heavy duty type intended for use on aircraft and on speedboats. Where it is important to limit the weight of the engine it is, of course, highly desirable to utilize cylinders having walls of minimum thickness, having in mind only the stresses and wear to which such walls are to be subjected in use and allowing for no weakening because of corrosion. The amount of corrosion which can occur varies widely and can hardly be predicted in ad Vance so that a very considerable uncertainty is thrown into the problem of design by this single factor unless means is employed to eliminate it completely, such as that above suggested, i. e., covering the cylinder wall surfaces of the water passages with a protective layer. It is, however, by no means a simple matter to prov de a protecof the problem and all that has heretofore been d scovered in the art of providing protective coatings, special problems arising from time to time which cannot be solved by known methods due to the presence of factors not before met with.

An internal combustion engine of special type has recently been developed for the propulsion of speedboats in the fabrication of which individually formed cylinders are utilized, each cylinder assembly preferabl comprising a cylinder proper formed of a low alloy steel and. a water jacket which comprises an envelope for the major portion of the cylinder wall defining, with the wall, a water space of annular cross section at least as long as the combustion chamber-and that portion of the cylinder in which the piston travels. The water jacket is conveniently fabricated of thin sheet metal and it is highly advantageous to form it of steel of corrosion resisting type such for instance as the steel which is commonly called stainless and which includes approximately 18% of chipmium and 8% of nickel. A most satisfactory way of attaching the stainless steeljacket to the wall of the cylinder is by welding and it is now common practice to so secure such a jacket in position, the welding being either gas or electric welding.

The water space of the cylinder is, after the jacket has been welded in place, completely closed save for the relatively small water inlet and outlet apertures and but little can be done after the assembly to effectively coat the outer surface of the cylinder, which is the surface to be eventually subjected to the corrosive action of the cooling water. Hence it is necessary to apply the protective coating to the wall of the cylinder prior to the time that the jacket is assembled and this in turn means, of course, that the coating material which is so applied, whatever it may be, must be able to withstand a substantial amount of heat without losing its protective properties, since heating of the cylinder at the ends of the water jacket will occur when the water jacket is attached to the cylinder by welding. It is furthermore essential that the coating material, whatever it may be, shall not be of such character that, when heated during the jacket welding operation, it will generate fumes which will attack theweld or the cylinder wall or the jacket while the cylinder wall metal or jacket metal are heated during the welding operation.

It has been found for instance that a coating of cadmium applied electrolytically to the wall surface of a low alloy steel cylinder is disturbedand broken down so as to be rendered ineffective by the heat incident to the welding of the jacket onto the cylinder and that such a layer is disadvantageously affected by the heat developed during the subsequent operation of the engine, particularly in the vicinity of the spark plugs. It has also heretofore been suggested that a coating of nickel upon the exterior surface of the cylinder wall might sufiice if covered in turn with a second coating of zinc, both coatings electrolytically deposited. In actual practice, however, this suggested method has been proven to be wholly ineffective, zinc vapors being generated because of the welding heat and these vapors attacking those portions of the stainless steel jacket which are raised to welding heat. apparently attacking the grain boundaries of the stainless steel and. creating an extremely brittle metal which caused failure at the welds even before the welds could be completed. Other types of coatings for the surfaces to be prot cted against corrosion were found to be ineffective for one reason or another and itwas only after long research that it was ascertained that a protective coating comprising an alloy of nickel and cadmium was entirely satisfactory in every respect, remaining intact and uninjured during the time of the original fabrication of the cylinder assembly and having the capacity to fully protect the cylinder wall against the corrosive action of the cooling water.

This improved process will now be described. A preferred embodiment of the engine cylinder construction contemplated by the invention is illustrated in the accompanying drawing, in which:

Figure, 1 is a view, in perspective and partly broken away, of the engine cylinder construction selected for disclosure by way of example; and

Figure 2 is a view showing a small portion of the wall of such cylinder, showing superposed thereon separate coatings of nickel and cadmium as originally applied and prior to the alloying of such coatings.

In the drawing the cylinder proper is indi cated at and is seen to include a cylinder wall H and head II which may advantageously be welded together or, if desired, formed as a single member and machined'to the shape in which it appears in the drawing. The cylinder wall I I, and the head i2, may be separately formed as castings of low alloy steel and welded together.

the cylinder head being a sand casting and the wall' a centrifugally formed casting. The water jacket is indicated at 13 and comprises a generally cylindrical member of corrosion resisting steel, the cylindrical ends of the jacket being welded, respectively, to ribs projecting outwardly from the cylinder wall H, a gas weld being indicated at H and an electrical seam weld at i5.

I The precise nature of the welding operation which is followed is not of the essence of the invention and any suitable welding method may be employed. In every instance, however, the metal at the ends of jacketl3 and the metal of the ribs of the cylinder body must be raised in temperature, in the vicinity of the weld, to welding heat in order to permit a satisfactory weld to be formed. The heat, of course, is largely localized but the parent metal of the cylinder will be highly heated for some distance from the actual weld and it is hence necessary for any coating layer which has been previously applied to the outer surface of the cylinder I I between the jacket attachment ribs to be able to withstand this welding heat without disintegration or deterioration. Otherwise, a band of unprotected metal would remain, adjacent each attachment rib, and these bands would be attacked by corrosive waters thus nullifying the attempt to protect the cylinder.

In the practice of the invention the outer wall surface Of the cylinder II has first deposited thereon by any suitable electrolytic method a layer of dull nickel, this layer being applied over all outer surfaces of the cylinder which cooling water may later reach during the operation of the engine of which the cylinder forms one element. The coating of nickel may vary in thickness from a minimum of .0002 inch upwardly and I have found in actual practice that a coating having a thickness of .0003 inch is satisfactory. Following the deposition of the layer of dull nickel upon the surface to be protected :1 second layer is deposited thereon completely covering the previously deposited nickel layer, this second layer comprising cadmium. and having a thickness not less than .0001 inch. A layer of cadmium which is .0003 inch in thickness is eminently satisfactory.

Following the deposition on the cylinder wall of the two successive layers of metal, the water jacket I3 is applied and is welded at its ends to ribs integral with the cylinder wall H and projecting laterally therefrom, the welds being either gas welds and involving the deposition of added weld metal, or electric Welds, involving the passage of an electric current and the subjection of the contacting metallic parts heated by such current to pressure. Satisfactory results can be obtained by either process and, of course, in either process the metal must be raised in temperature to welding heat in order that fusion may occur. At the completion of the welding operation it remains to effect the alloying of the previously deposited layers of nickel and cadmium and this is accomplished by placing the assembly in a furnace and uniformly raising its temperature to 850 F., holding the assembly at that temperature for a minimum period of approximately thirty minutes and thereafter permitting it to cool slowly. This temperature may be varied somewhat but in every case must be above that at which cadmium fuses and, as a result, the cadmium and nickel coatings will be alloyed together to form the composition coating found to be so highly resistant to the action of oxygencontaining cooling water. The specified temperature is below that at which nickel melts or fuses but, on the other hand, is also sufficiently high to permit the assembly to relieve itself of the residual stresses in the welds caused by the heating and subsequent rapid cooling of the weld metal and portions of the parent metal adjacent the welds. It may sometimes be desirable to hold the temperature of the assembly at approximately 850 F. for a period substantially longer than thirty minutes. to insure that the stresses due to welding are completely relieved,

During this heating operation, which is preferably carried out in a neutral or inert atmosphere, no gases having a tendency to attack the stainless steel jacket or cylinder wall, when these parts are raised to welding heat, are developed. The resulting protective layer of alloy is continuous over the entire surface of the cylinder which is exposed to the corrosive action of water and the protection afforded thereby is, to all intents and purposes, perfect. In laboratory tests, aerated water passed over such protected surfaces for long periods of time have failed to have any injurious effect and the performance of the cylinder assemblies in the field under adverse conditions has been gratifying. Without such protecting layer corrosion rapidly proceeds and in a relatively short time pits of substantial depth are formed in the cylinder walls. The invention, therefore, is an important improvement in the fabrication of internal combustion engine cylinders of the light-weight type.

While it is preferred that the application of heat be postponed until welding has been completed, so as to comprise the final step of the process of assembly and thereby simultaneously accomplishing the alloying of the two electrolytically deposited layers and relieving the assembly of stresses, thus shortening the overall process of manufacture, it is nevertheless a matter of choice whether the alloying of the metal layers by the application of heat be carried out at the same time that the stress relieving operation is effected, if stress relief is necessary, or at an earlier time, and in some instances it may be preferred to alloy the nickel and cadmium prior to application of the water jacket.

Having thus described the invention, what is claimed as new and desired to besecured by Letters Patent is:

1. The method of fabricating an engine cylinder assembly, which includes a cylinder and a separately formed Water jacket, comprising depositing a continuous coating of nickel upon that portion of the outer surface of the cylinder which would, unless protected, be exposed to the actionof a cooling fluid, depositing upon said coating of nickel a coextensive coating of cadmium, welding the water jacket to the cylinder so as to envelop the coated surface thereof, and thereafter heating th assembly to a temperature of approximately 850 F. and permitting the same to cool.

2. The method of fabricating an engine cylinder assembly, which includes a cylinder and a separately formed water jacket, comprising depositing a continuous coating of nickel upon that portion of the outer surface of the cylinder which would, unless protected; be exposed to the action of a cooling fluid, depositing upon said coating of nickel a coextensive coating of cadmium, welding the water jacket in position on the cylinder so as to envelop the coated surface thereof, and thereafter heating the assembly to a temperature higher than that at which cadmium melts, to alloy the cadmium and nickel.

3. The method of fabricating an engine cylinder assembly, which includes a cylinder and a separately formed water Jacket, comprisingdepositing a continuous coating of nickel upon that portion of the outer surface of the cylinder which would, unless protected, be exposed to the action of a cooling fluid, depositing upon said coating of nickel a coextensive coating of cadmium, securing the water jacket in position on the cylinder so as to envelop the coated surface thereof, and thereafter heating the assembly to a temperature higher than that at which cadmium melts, to alloy the cadmium and nickel.

4. The method of fabricating an engine cylinder assembly which includes a steel cylinder and a separately formed steel water jacket containing nickel and chromium in suflicient amounts to render the same corrosion resistant, comprising depositing a continuous coating of nickel upon that portion of the outer surface of the cylinder which would, unless protected, be exposed to the action of a cooling fluid, depositing upon said coating of nickel a coextensive coating of cadmium, welding the water jacket in position on the cylinder so as to envelop the coated surface thereof, and thereafter heating the assembly to a temperature sufficiently high to alloy the cadmium and nickel and relieve the stresses in and adjacent the weld which have resulted from the welding operation.

5. An engine cylinder assembly comprising a cylinder and a water jacket enveloping the same and defining, with the cylinder, a channel for a cooling liquid, that portion of the outersurface of the cylinder which would otherwis be exposed to the corrosive action of the cooling liquid being covered and protected by a coating of an alloy of nickel and cadmium.

6. An engine cylinder assembly comprising a steel cylinder and a sheet metal water jacket of steel containing chromium and nickel in sufficient amounts to render the same corrosion resistant, the water jacket enveloping a portion of the cylinder and being welded thereto, that portion of the outer surface of the cylinder which would otherwise be exposed th the corrosive action of the cooling liquid passing through the channel defined by cylinder wall and water jacket being covered and protected by a coating of an alloy of nickel and cadmium.

7. The method of fabricating an engin cylinder assembly, which includes a cylinder and a separately formed water jacket, comprising depositing a continuous coating of nickel upon that portion of the outer surface of the cylinder which would, unless protected, be exposed to the action of a cooling fluid, depositing upon said coating of nickel a coextensive coating of cadmium, and thereafter completing the assembly by securing the water Jacket in position on the cylinder so as to envelop the coated surface thereof and heating the cylinder to a temperature higher than that at which cadmium melts to alloy the cadmium and mckel.

, RALPH E. VAN DEVENTER. 

